1. Field of the Invention
The present invention relates to a valve operating system for an engine including a biasing means for biasing a rocker arm and a support portion for the biasing means.
2. Description of the Related Art
There is a known valve operating system for an engine, which includes a biasing member for biasing a rocker arm to drive an intake valve or an exhaust valve of the engine toward a cam or toward the valve. In addition, a valve operating system for an engine including a lift-amount changing member that can change the lift amount of an intake valve or an exhaust valve of an engine is disclosed in Japanese Patent Application Laid-open No. 8-232623. In this type of the valve operating system for the engine, a driving rocker arm and a free rocker arm are disposed between a valve and a camshaft so the swinging movement of the free rocker arm is transmitted through the driving rocker arm to the valve by connecting the driving rocker arm and the free rocker arm to each other by a connection switchover mechanism. The swinging movement of the driving rocker arm is transmitted to the valve by disconnecting the free rocker arm from the driving rocker arm using the connection switchover mechanism. In order to prevent the free rocker arm, which is disconnected from the valve, from being moved away from the cam when the connection between both rocker arms is released, the free rocker arm is biased toward the cam by a lost motion mechanism.
The valve operating system described in Japanese Patent Application Laid-open No. 8-232623 has several drawbacks. For example, an upper surface of the camshaft supported in a camshaft holder mounted in a cylinder head is retained by a camshaft cap. Also, the lost motion mechanism is disposed above a rocker arm shaft supported above the camshaft cap. As a result, the lost motion mechanism protrudes significantly upwards, resulting in an increase in the vertical dimension of the engine. Moreover, the valve operating system includes a holder that exclusively supports the lost motion mechanism, resulting in an increase in the overall number of parts. In an attempt to avoid these drawbacks, it was believed that the lost motion mechanism could be disposed on the camshaft holder or the camshaft cap below the rocker arm shaft. However, a bolt that fastens the camshaft cap to the camshaft holder is already disposed in such a location and would result in an increase in the number of parts. Moreover, there is a problem that the degree of freedom of the design for a position where the lost motion mechanism is disposed is limited since interference between the lost motion mechanism and the bolt is to be avoided.
It is an object of the present invention to overcome the above-discussed drawbacks of the related art.
It is also an object of the present invention to reduce the number of parts of the engine, including the biasing means that biases the rocker arm and the support portion for the biasing means, as well as to reduce the vertical dimensions of the engine.
To achieve the above object, there is provided a valve operating system for an engine that includes a camshaft axially inserted into a camshaft holder formed in a cylinder head. A rocker arm is driven by the camshaft and a valve is driven by the rocker arm. The camshaft holder is integrally formed with a support portion, for a biasing member that biases the rocker arm toward the camshaft or the valve.
With the above arrangement, the support portion for the biasing member is integrally provided on the camshaft holder. Accordingly, a holder exclusive for supporting the biasing member is not required, which results in a reduction in the overall number of parts. In addition, because the camshaft is axially inserted into the camshaft holder, a camshaft cap that supports the camshaft and a bolt that fastens the camshaft cap to the camshaft holder are not required, which reduces the overall number of parts. Furthermore, the present invention also leads to an increase in degree of freedom of the design for positions where the biasing member can be disposed since there is very little possibility that the support portion for the biasing member will interfere with the bolt.
There is also provided a valve operating system for an engine that includes a camshaft axially inserted into a camshaft holder formed in a cylinder head. A valve is driven by a rocker arm. A lift-amount changing means, which is capable of changing a lift amount of the valve, includes a free rocker arm adapted to abut against a first cam, a biasing member for biasing the free rocker arm in a direction wherein the free rocker arm can abut against the first cam, a driving rocker arm adapted to abut against a second cam to drive the valve, and a connection switchover mechanism for connecting or disconnecting the free rocker arm and the driving rocker arm. The camshaft holder below the free rocker arm is integrally provided with a support portion for the biasing member.
With the above arrangement, the support portion for the biasing member is integrally provided on the camshaft holder below the free rocker arm. Hence, the vertical dimension of the engine is reduced as compared with a case where the support portion is provided above the free rocker arm. Moreover, a holder exclusive for supporting the biasing member is not required, which reduces the overall number of parts. In addition, the camshaft is axially inserted into the camshaft holder mounted in the cylinder head. Hence, a camshaft cap that supports the camshaft and a bolt that fastens the camshaft cap to the camshaft holder are not required, which decreases the overall number of parts, but also increases, in degree of freedom of the design, the overall number of positions where the biasing member can be disposed because there is very little possibility that the support portion for the biasing member will interfere with the bolt.
The support portion can also include a recessed portion formed on an upper surface of the camshaft holder.
With the above arrangement, the support portion for the biasing member includes the recessed portion formed on the upper surface and hence, a tool for processing the support portion is difficult to interfere with another member and thus, it is easy to process the support portion.
Furthermore, a side face of the support portion and a seat face for a bolt that fastens the cylinder head to a cylinder block can be connected to each other by a connecting wall.
With the above feature, the side face of the support portion for the biasing member and the seat face for the bolt for fastening the cylinder head to the cylinder block are connected to each other by the connecting wall. Hence, the rigidity of the support portion is increased, leading to an increase in support rigidity of the biasing member.
Additionally, the support portion and a rocker arm shaft support portion that supports a rocker arm shaft can be connected to each other by a connecting wall.
With the above arrangement, the support portion for the biasing member and the rocker arm shaft support portion for supporting the rocker arm shaft are connected to each other by the connecting wall. As a result, both the support portion and the rocker arm shaft support portion are effectively reinforced, leading to an increase in support rigidity of the support portion and the rocker arm shaft support portion.
It should be noted that the support portion can also include a recessed portion, a bottom of which is inclined in a direction away from the camshaft.
With the above arrangement, the bottom of the support portion for the biasing member that includes the recessed portion is inclined in a direction away from the camshaft. Accordingly, the peripheral wall of a journal support bore defined in the camshaft holder is increased, leading to an increase in support rigidity of the camshaft.
At least a portion of the recessed portion of the support portion can be formed within a width of the camshaft holder in a direction of the camshaft.
With the above arrangement, at least a portion of the support portion including the recessed portion is formed within the width of the camshaft holder in the direction of the camshaft, resulting in a reduction of the dimension of the valve operating system in the direction of the camshaft.
The intake valve for each embodiment corresponds to the valve of the present invention; a flat face for each embodiment corresponds to the rocker arm shaft support portion of the present invention; a driving intake cam and a stopping intake cam for each embodiment corresponds to the first cam and the second cam of the present invention, respectively; and a spring for each embodiment corresponds to the biasing member of the present invention.